[84959] in North American Network Operators' Group
Re: Weird DNS issues for domains
daemon@ATHENA.MIT.EDU (Crist Clark)
Thu Sep 29 14:03:51 2005
Date: Thu, 29 Sep 2005 11:00:16 -0700
From: Crist Clark <crist.clark@globalstar.com>
In-reply-to: <Pine.NEB.4.63.0509291326390.8521@server.duh.org>
To: Todd Vierling <tv@duh.org>
Cc: John Dupuy <jdupuy-list@socket.net>, nanog@nanog.org
Reply-To: crist.clark@globalstar.com
Errors-To: owner-nanog@merit.edu
Todd Vierling wrote:
> On Thu, 29 Sep 2005, John Dupuy wrote:
>
>
>>If you are talking about strictly http, then you are probably right. If you
>>are hosting any email, then this isn't the case. A live DNS but dead mail
>>server will cause your mail to queue up for a later resend on the originating
>>mail servers. A dead DNS will cause the mail to bounce as undeliverable.
>
>
> If a mail server is bouncing immediately on a DNS SERVFAIL (which is what
> you'll get when a remote DNS server is down), then that mail server is badly
> broken and will break quite a bit during tier1 failure situations.
>
> Failure to resolve != resolves to NXDOMAIN/empty. A failure to resolve
> (SERVFAIL) should result in the same queueing behavior that the remote SMTP
> server uses for failure to establish a TCP connection.
The problem I've seen is when an SMTP server does not accept emails
which have non-resolvable MAIL FROM domain. When the sender is a dumb
SMTP client, not an MTA, this can cause problems.
(I noticed this happen to a high traffic customer who had both of their
DNS servers in the same /24 located in Slidell, LA. Needless to say, they
were down for more than a few hours when Katrina rolled through.)
--
Crist J. Clark crist.clark@globalstar.com
Globalstar Communications (408) 933-4387
